Out of bounds exception in B Console

When typing RSQRT(real(2)) in the B Console in EventB mode, I got this exception:

[2020-11-10 11:55:48,530, 53150 ms] "JavaFX Application Thread" [ERROR] de.prob2.ui.ProB2.lambda$startInBackground$5(ProB2.java:188): Uncaught exception on thread Thread[JavaFX Application Thread,5,main]
java.lang.StringIndexOutOfBoundsException: begin 8, end 0, length 0
at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3734)
at java.base/java.lang.String.substring(String.java:1903)
at java.base/java.lang.String.substring(String.java:1876)
at de.prob2.ui.consoles.Console.getInput(Console.java:425)
at de.prob2.ui.consoles.Console.handleEnter(Console.java:263)
at de.prob2.ui.consoles.Console.lambda$setEvents$15(Console.java:119)
at org.fxmisc.wellbehaved.event.InputMap.lambda$consume$2(InputMap.java:256)
at java.base/java.util.Optional.map(Optional.java:258)
at org.fxmisc.wellbehaved.event.PatternActionMap.lambda$forEachEventType$1(InputMap.java:414)
at org.fxmisc.wellbehaved.event.InputHandlerMap.lambda$null$0(InputHandlerMap.java:22)
at org.fxmisc.wellbehaved.event.InputHandler.handle(InputHandler.java:50)
at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$KeyHandler.process(Scene.java:4058)
at javafx.graphics/javafx.scene.Scene$KeyHandler.access$1500(Scene.java:4004)
at javafx.graphics/javafx.scene.Scene.processKeyEvent(Scene.java:2121)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2595)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:217)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$KeyEventNotification.run(GlassViewEventHandler.java:149)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleKeyEvent$1(GlassViewEventHandler.java:248)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:247)
at javafx.graphics/com.sun.glass.ui.View.handleKeyEvent(View.java:547)
at javafx.graphics/com.sun.glass.ui.View.notifyKey(View.java:971)